River valleys are thickly populated because people need water to wash clothes,water for drinking,water for taking bath,water for cooking food. especially river valleys are populated by villager because there is no much fecilities of water in villages till now.
1
Akshaya Sayeerajan answered this
this is because water in the river may help to do many activities in our life.
1
Jivitesh Karol answered this
Nowadays, people take to smart methods and migrate or travel to places of agricultural and water prosperity. These conditions can be satisfied by going to river valleys and settling down there. They go here, as droughts don't occur regularly and the people will have plenty of good to eat. Smart choices are not uncommon in today's world as people study hard enough to settle down in river valleys and build their shelters over there.